Yaris Antenna
 

How much aerodynamic advantage will I get if I switch my stock Yaris antenna with a low/aero one?

It's likely to be negligible. Unless you combined this with many other aero mods, I don't think you would see any change in millage.

I mounted my antenna on the inside of my windshield so it contributes zero aero drag. The relocation produced only a slight drop in reception sensitivity.

I'm thinking that if you have a standard car then it'll make no measurable difference. But if you have a highly modified mpg machine and are already getting galactic mileage, then it may make a few mpg appear.

ollie